engleski

Interspecies representational difference analysis in study of genome evolution in genus Quercus

Eleven oak species of different phylogenetic positions and geographic repartition have very similar genome sizes (1.88-2.00 pg/2C) and almost identical karyotypes. The number and position of some cytogenetic markers (heterochromatic bands and ribosomal loci) are also highly conserved between their karyotypes. In the absence of any karyotype differentiation, the genome differentiation on molecular level was searched for using a relatively novel approach of the technic Representational Difference Analysis (RDA). The method is based on subtractive hybridisation of two different genomes (the driver genome against the tester genome) which permits isolation of the specific DNA sequences to only one genome (the tester genome), thus yielding DNA differences between the two. Quercus robur (common oak) was chosen as a tester genome and Q. suber (cork oak) was chosen as a driver genome. A library of 400 RDA fragments specific to Q. robur was obtained after one step experiment and cloning. Several RDA fragments were analyzed for their organization and copy number in the genome of Q. robur ; they all belong to repetitive dispersed DNA sequences present in 100 to 700 copies. In situ hybridization of the same fragments to chromosomes of Q. robur confirmed their presence throughout the genome without clustering in specific chromosome loci. A search for homologies between the RDA fragments and sequences in GeneBank revealed similarities of all RDA fragments with known copia/Tyl-like retrotransposons. The same RDA fragments were tested for their presence/absence in the genomes of other oak species of the sample in order to examine the evolutionaly dynamics of these sequences.

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